Menstrual Cycle Length Calculator

About This Tool

The online Menstrual Cycle Length Calculator is used to calculate your menstrual cycle length based on the first day of your last two menstrual period.

Many people believe the average menstrual cycle takes 28 days, but a large study of more than 30,000 cycles from more than 2300 women showed that the mean cycle length was 29.1 days. The normal menstrual cycle ranges from 25 to 35 days. The variability of menstrual cycle lengths is highest for women under 25 years of age and is lowest, that is, most regular, for ages 35 to 39. Subsequently, the variability increases slightly for women aged 40 to 44.